The invention relates to an extrusion tool for a film blow head of a tubular extrusion system for extrusion of a tube from a plastic melt with a tool body which comprises a melting channel for the configuration of the tube, wherein the tool body comprises a collar region with an outlet opening for the configured tube. Further, the invention relates to a method for the production of a plastic tube which is extruded from an extrusion tool of a film blow head. Further, the invention relates to an extruded plastic film, which is configured from a polyethylene.
From document U.S. Pat. No. 3,709,290 an extrusion tool for a film blow head of a tubular extrusion system is known. It has been shown that the surface properties of the extrudate in general show, that with low shear stress the escape of the extrudate (plastic melt) is smooth and glossy. If said tension comprises a critical value the extrudate shows a loss of surface gloss. Further, it has been shown that the extrusion of plastic films, blown films, which can be particularly configured in a multi-layered manner, with certain raw material combinations of the extrudate often structured inconsistencies at the film surface, tube surface, occur by flow dependent interactions between the flowing polymer and the melting channel wall in the collar area. These existing surface inconsistencies are also called surface melt fracture which is mainly restricted to the extrudate surface. Particularly, the often used LLDPE or mLLDPE plastics at the outer and inner layer are often not extrudable in a proper film optic without dosing additional so called process aid means (for example AMF: anti melt fracture). This process aid means serve as additives in order to for example increase the gliding properties of the plastic melt in the wall area of the melting channel, particularly to reduce the friction at the melting channel wall. These additives reduce melting fractures in the extrudates. Disadvantageously such additives are expensive and the additional costs, according to the desired concentration, avoid its use in plastics, like for example LLDPE, which for example can be intended for articles of daily use application. Further the said additives or process aid means can also influence the rheological properties of the plastic of the extruded film or tube. Further, it has been shown that in overage amounts the used additives can influence critical tube and film properties in an opposing direction like gloss, haze, transparency or weldability of the film.